Silver halide color photosensitive materials are known in this field of art, and the color diffusion transfer method which comprises producing or releasing imagewise a diffusible dye, and then diffusion transferring the same to a dye fixing material (an image receiving material) is also known in this field of art.
With respect to methods for obtaining color images by heat development, many methods have been suggested. With respect to methods for obtaining color images by joining an oxidation product of a developer with a coupler, p-phenylenediamine reducing agents and phenolic or active methylene couplers are suggested in U.S. Pat. No. 3,531,286, p-aminophenol type reducing agents are suggested in U.S. Pat. No. 3,761,270, sulfonamidophenol type reducing agents are suggested in Belgian Patent No. 802,519 and Research Disclosure (September 1975), pages 31 and 32 and combination of sulfonamidophenol type reducing agents and 4-equivalent couplers are suggested in U.S. Pat. No. 4,021,240.
However, these methods have the drawback that since an image of reduced silver and a color image are produced simultaneously in the exposed part after heat development, the color image becomes turbid.
To overcome the drawback, a method has been suggested wherein the silver image is removed by liquid treatment or a method has been suggested wherein only the dye is transferred to another layer such as a sheet having an image receiving layer, but these methods have the drawback that it is difficult to transfer only the dye, i.e., separately from unreacted substances.
Further, in the above methods, generally the time required for the development is relatively long, and disadvantageously the image obtained is undesirably high in fog and low in density.
To obviate these drawbacks, there have been suggested a method wherein a mobile dye is released imagewise by heating, and the mobile dye is transferred to a dye fixing element having a mordant by a solvent such as water, a method where the dye is transferred to a dye fixing element by a high boiling point organic solvent, a method wherein the dye is transferred by a hydrophilic thermal solvent contained in a dye fixing element, a method wherein the mobile dye is heat-diffusible or sublimable and is transferred to a dye receiving material such as a support, and other methods (see U.S. Pat. Nos. 4,463,079, 4,474,867, 4,478,927, 4,507,380, 4,500,626 and 4,483,914, Japanese Patent Application (OPI) Nos. 149046/83, 149047/83, 152440/84, 154445/84, 165054/84, 180548/84, 168439/84, 174832/84, 174833/84, 174834/84 and 174835/84, etc., (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Methods wherein heat development is carried out in the presence of a small amount of water, and the released dye is transferred so that the development may be promoted, the temperature of the development may be lowered and the treatment may be simplified are disclosed in Japanese Patent Application (OPI) Nos. 218443/84 and 238056/86. In these methods, although a base is contained in a dye fixing element, since the film quality tends to be deteriorated and there is a safety problem, a method disclosed in European Patent Application No. 210,660A uses a complex formation reaction to give off a base.
In these image forming methods, it is required that after the dye is moved, the photosensitive element and the dye fixing element have to be separated (peeled). Therefore, the quality of the surface of the dye fixing element should be such that the surface of the dye fixing element can be brought into firm contact with the photosensitive element to such a degree to allow sufficient migration of the mobile dye, the migration of the dye should not be hampered, the separation, that is, peeling after the transfer, can be made smoothly, and the surface of the dye fixing element should not be roughened when the peeling is effected.
As one means for allowing the peeling to be effected smoothly, there is a method of increasing the hardness of the coated film of the photosensitive element and/or the dye fixing element. However, although smoothness of peeling can be improved to a some extent by this method, there is a problem in that the diffusion of a dye is hampered and the transfer is inefficiently made.
In the case as described, for example, in U.S. Pat. No. 4,500,626, Japanese Patent Application (OPI) Nos. 218443/84 and 238056/86 where small amount of water is supplied to the photosensitive element and/or the dye fixing element, and heat development is carried out or the dye is transferred by heating, particularly the photosensitive element and the dye fixing element are liable to adhere and the peeling becomes difficult, and in this case if the hardness of the coated film is increased, it takes a longer period of time for the supplied water to penetrate the coated film completely, and as a result the process of image formation cannot be made in a short period of time. Furthermore, if the photosensitive element or the dye fixing element is fed and conveyed as a sheet, troubles such as malfunction of feeding and conveyance due to insufficient slip or jamming trouble under high humidity conditions occur.